Embodiments of the invention concern the field of optical systems, more specifically the field of lenses and manufacturing such lenses. Embodiments of the invention relate to wafer scale optics, more specifically to wafer scale lens designs that may be used in lens arrangements or optical systems, e.g. in digital cameras in mobile phones, personal digital assistants and the like, especially in combination with CMOS image sensors.
In the field of wafer scale optics lenses are manufactured by providing a UV curable polymer material onto a thick glass substrate and shaping the polymer material into a desired lens form. The polymer may be deposited either on one side or on both sides of the glass substrate. A plurality of such lens wafers are stacked on each other, either directly or by means of one or more spacer wafers which may be glass or polymer substrates comprising holes. Thus, the respective lenses are arranged with a distance to the imaging plane. Then, the wafer is diced and the respective optics are mounted to an imaging sensor.
This approach is disadvantageous as for mechanical and structural reasons the amount of high refractive index material, i.e. materials having a refractive index n of about 1.5 vs. n=1 of air, (e.g. the substrates which form parallel plates) within the imaging beam path is higher as it is desired by the optical design. This reduces the image quality and necessitates more lenses and/or lenses having a more complicated shape within the stack to compensate for the reduced image quality. Thus, the adaptation of “classic” lens designs and the use of the design rules which apply for these classic lens designs which avoid the occurrence of specific imaging errors cannot be used in the design of such wafer scale lenses.
The just mentioned wafer scale optics and sandwiches thereof may be used in digital cameras and, by their nature, incorporate substrates (wafers). From the manufacturing perspective it is actually advantageous that these substrates are comparatively thick compared to the (UV-polymer replicated) lenses which are formed on top of the substrate or on both sides of the substrate. However, this is contradiction to lens arrangements observed in classical objective designs where for example arrangements of one or several thin but strongly bent meniscuses are applied in order to reduce aberrations and especially to obtain a small astigmatism. This is a drawback of state-of-the-art wafer scale lens designs as due to the evident problem of astigmatism in these designs their optical performance is poor although much more complex (highly aspheric) lens shapes are applied. The problem of thick substrates is especially evident for the above mentioned meniscus lenses, which is the lens that has lens surfaces which are curved into the same direction. As mentioned above, in conventional optical systems a strong curvature of the meniscus is desired, however, applying this design rule to wafer scale optics will necessitate the provision of a glass substrate between the opposing lens areas. In view of the strong curvature of the opposing surfaces of the meniscus a high thickness is necessitated so that the lens will lose its optical advantages.
An alternative approach for manufacturing lenses on a wafer scale is to emboss the complete lens wafer from a polymer material which allows lenses to be generated which are very thin. However, this approach is disadvantageous, as the wafer itself is not a stable support device (e.g. a stable glass support). This instable support will result in inhomogeneities regarding the thickness and the bending of the wafer. Also shrinkage of the wafer is observed resulting in a lateral uncertainty. These effects can be severe such that a plurality of wafers or plates cannot be stacked on top of each other.
Another approach known in the art for manufacturing lenses is the injection molding of lenses. However, the procedural overhead for generating lenses using injection molding in terms of machinery and in terms of process steps is disadvantageous. Further, no manufacturing on a wafer scale is possible.